Datasheet LT1175 (Analog Devices) - 11
| Manufacturer | Analog Devices |
| Description | 500mA Negative Low Dropout Micropower Regulator |
| Pages / Page | 20 / 11 — APPLICATIONS INFORMATION. Figure 3 |
| File Format / Size | PDF / 221 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Figure 3
Model Line for this Datasheet
- LT1175CN8#PBF LT1175CN8-5#PBF LT1175CQ#PBF LT1175CQ#TRPBF LT1175CQ-5#PBF LT1175CQ-5#TRPBF LT1175CS8#PBF LT1175CS8#TRPBF LT1175CS8-5#PBF LT1175CS8-5#TRPBF LT1175CST-5#PBF LT1175CST-5#TRPBF LT1175CT#06PBF LT1175CT#PBF LT1175CT-5#06PBF LT1175CT-5#PBF LT1175IN8#PBF LT1175IN8-5#PBF LT1175IQ#PBF LT1175IQ#TRPBF LT1175IQ-5#PBF LT1175IQ-5#TRPBF LT1175IS8#PBF LT1175IS8#TRPBF LT1175IS8-5#PBF LT1175IS8-5#TRPBF LT1175IST-5#PBF LT1175IST-5#TRPBF LT1175IT#PBF LT1175IT-5#PBF LT1175MPQ#PBF LT1175MPQ#TR LT1175MPQ#TRPBF LT1175MPQ-5 LT1175MPQ-5#PBF LT1175MPQ-5#TRPBF LT1175MPS8#PBF LT1175MPS8#TRPBF LT1175MPS8-5 LT1175MPS8-5#PBF LT1175MPS8-5#TRPBF
Text Version of Document
LT1175
APPLICATIONS INFORMATION
GND LT1175 + 3.8V – R1 A1 COUT + LOAD ESR R2 SENSE Q2 AC FEEDFORWARD C OUTPUT F PATH 20pF OUTPUT RC 0.5Ω NEGATIVE DC PARASITIC FEEDBACK COLLECTOR AT LIGHT Q3 Q1 RESISTANCE LOADS R POWER N TRANSISTOR RLIM CURRENT LIMIT SENSE RESISTOR 1175 F03 VIN
Figure 3
This condition can occur with ceramic or fi lm capacitors The end result of all this attention to loop stability is that which often have an ESR under 0.1Ω. With previous de- the output capacitor used with the LT1175 can range in signs, the user was forced to add a real resistor in series value from 0.1μF to hundreds of microfarads, with an ESR with the capacitor to guarantee loop stability. The LT1175 from 0Ω to 10Ω. This range allows the use of ceramic, uses a unique AC feedforward technique to eliminate solid tantalum, aluminum and fi lm capacitors over a wide this problem. CF is a conventional feedforward capacitor range of values. often used in regulators to cancel the pole formed by the The optimum output capacitor type for the LT1175 is output capacitor. It would normally be connected from the still solid tantalum, but there is considerable leeway in regulated output node to the feedback node at the R1/R2 selecting the exact unit. If large load current transients junction or to an internal node on the amplifi er as shown. are expected, larger capacitors with lower ESR may be In this case, however, the capacitor is connected to the needed to control worst-case output variation during internal structure of the power transistor. RC is the unavoid- transients. If transients are not an issue, the capacitor able parasitic collector resistance of the power transistor. can be chosen for small physical size, low price, etc. Access to the node at the bottom of RC is available only Concerns about surge currents in tantalum capacitors are in monolithic structures where Kelvin connections can not an issue for the output capacitor because the LT1175 be made to the NPN buried collector layer. The loop now limits inrush current to well below the level which can responds as if RC were in series with the output capacitor cause capacitor damage. Surges caused by shorting the and good loop stability is achieved even with extremely regulator output are also not a problem because tantalum low ESR in the output capacitor. 1175ff 11
APPLICATIONS INFORMATION
GND LT1175 + 3.8V – R1 A1 COUT + LOAD ESR R2 SENSE Q2 AC FEEDFORWARD C OUTPUT F PATH 20pF OUTPUT RC 0.5Ω NEGATIVE DC PARASITIC FEEDBACK COLLECTOR AT LIGHT Q3 Q1 RESISTANCE LOADS R POWER N TRANSISTOR RLIM CURRENT LIMIT SENSE RESISTOR 1175 F03 VIN
Figure 3
This condition can occur with ceramic or fi lm capacitors The end result of all this attention to loop stability is that which often have an ESR under 0.1Ω. With previous de- the output capacitor used with the LT1175 can range in signs, the user was forced to add a real resistor in series value from 0.1μF to hundreds of microfarads, with an ESR with the capacitor to guarantee loop stability. The LT1175 from 0Ω to 10Ω. This range allows the use of ceramic, uses a unique AC feedforward technique to eliminate solid tantalum, aluminum and fi lm capacitors over a wide this problem. CF is a conventional feedforward capacitor range of values. often used in regulators to cancel the pole formed by the The optimum output capacitor type for the LT1175 is output capacitor. It would normally be connected from the still solid tantalum, but there is considerable leeway in regulated output node to the feedback node at the R1/R2 selecting the exact unit. If large load current transients junction or to an internal node on the amplifi er as shown. are expected, larger capacitors with lower ESR may be In this case, however, the capacitor is connected to the needed to control worst-case output variation during internal structure of the power transistor. RC is the unavoid- transients. If transients are not an issue, the capacitor able parasitic collector resistance of the power transistor. can be chosen for small physical size, low price, etc. Access to the node at the bottom of RC is available only Concerns about surge currents in tantalum capacitors are in monolithic structures where Kelvin connections can not an issue for the output capacitor because the LT1175 be made to the NPN buried collector layer. The loop now limits inrush current to well below the level which can responds as if RC were in series with the output capacitor cause capacitor damage. Surges caused by shorting the and good loop stability is achieved even with extremely regulator output are also not a problem because tantalum low ESR in the output capacitor. 1175ff 11